Field of the Invention
This invention relates generally to a converging-diverging nozzle for providing reduced temperature cooling air and, more particularly, to a converging-diverging nozzle positioned within a cooling fluid flow path in a turbine section of a gas turbine engine for providing reduced temperature cooling air for cooling ring segments.
Discussion of the Related Art
The worlds energy needs continue to rise which provides a demand for reliable, affordable, efficient and environmentally-compatible power generation. Gas turbine engines are one known machine that provide efficient power, and often have application for electric generators in a power plant, or engines in an aircraft or a ship. A typically gas turbine engine includes a compressor section, a combustion section and a turbine section. The compressor section provides a compressed air flow to the combustion section where the air is mixed with a fuel and ignited to generate a working gas typically having a temperature above 1300° C. The working gas expands through the turbine section and is guided across blades by associated vanes. As the working gas passes through the turbine section, it causes the blades to rotate, which in turn causes a shaft to rotate, thereby providing mechanical work.
The temperature of the working gas is tightly controlled so that it does not exceed some predetermined temperature for a particular turbine engine design because to high of a temperature can damage various parts and components in the turbine section of the engine. However, it is desirable to allow the temperature of the working gas to be as high as possible because the higher the temperature of the working gas, the faster the flow of the gas, which results in a more efficient operation of the engine.
In certain gas engine turbine designs, a portion of the compressed air flow is also used to provide cooling for certain components in the turbine section, typically the vanes, blades and ring segments. Thus, the more cooling and/or the more efficient cooling that can be provided to these components allows the components to be maintained at a lower temperature, and thus the higher the temperature of the working gas can be. In other words, by reducing the temperature of the compressed gas, less compressed gas is required to maintain the part at the desired temperature, resulting in a higher working gas temperature and a greater power and efficiency from the engine. Further, by using less cooling air at one location in the turbine section, more cooling air can be used at another location in the turbine section. For example, in one known turbine engine design, 80% of the compressed air flow is mixed with the fuel to provide the working gas and 20% of the compressed air flow is used to cool the turbine section parts. If less of that cooling air is used at one particular location as a result of the cooling air being lower in temperature, then more cooling air can be used at other areas in the turbine section for increased cooling.